“I found unusual patterns of
low energy radiation, well below ionising frequencies, coming from
the solar system I’ve been examining.”

“You’ve ruled out it
coming from the star, I suppose?”

“Yes – that emits
fairly normal levels of radiation of all frequencies so far as I can
tell, no particular patterns beyond flares, bursts, that sort of
thing. These are very specific, very complex patterns, unlike
anything of a known natural origin.”

“That could be just the sign
life we’ve been looking for. Weren’t there some promising
looking large gaseous planets in the solar system that you were
looking at?”

“Yes, that’s the
trouble. It’s not coming from one of the gaseous planets. It’s
coming from a small, rocky planet much nearer the star.”

“A rocky planet? Are you
sure?”

“Yes. I thought that it was
one of the gaseous planets, too, until I observed that all the
signals were blocked when one of those very gaseous planets passed in
front of its orbit, for them only to come back again the moment that
it passed.”

“It’s possible, I
suppose, that life might form on a rocky planet in the right
conditions, although it’d be very difficult.”

“I wondered about that. But
this planet is far too close to the star. The temperatures would be
too high, even at the poles: well above the boiling point of
nitrogen.”

“Could it be tidally locked?
If the side of the planet that always faces away from the sun had
large pools of liquid nitrogen on its surface, then –”

“It can’t be tidally
locked; the orbit’s all wrong, I checked that, too. Every part
of that planet will be exposed to the heat from that star so often
that there won’t be any liquid nitrogen anywhere.”

“It’s hard to see how
life could have evolved without liquid nitrogen.”

“And there’s more.
Although it’s not a gaseous planet, it seems to be surrounded
by a huge cloud of gas. That’d make the planet even hotter –
even mercury would melt on its surface.”

“That is hot.”

“Yes – and the
composition of the gas: the spectrum analysis shows that it’s
mostly nitrogen, but there’s another gas in there as well:
oxygen.”

“Oxygen? That’s highly
reactive. That’d tear apart the delicate molecules on which
life is based given half a chance. How much of it is there?”

“About a fifth of the gas
cloud seems to be oxygen.”

“A fifth? That’d
destroy any known living organism in seconds. But perhaps there are
some extremophiles living near the poles that have evolved to block
out all the oxygen and tolerate the extreme heat?”

“Possibly. But there’s
another problem. Judging by the density calculations, the planet
seems to be made mainly of iron.”

“Iron? That’s harmless
enough.”

“Of itself, yes. But the
planet’s orbit is perturbed. It doesn’t match what I’d
expect if the planet were solid.”

“What’s the
significance of that”?

“One thing that we know about
these rocky planets is that the younger ones can have liquid
interiors. They cool over time and solidify, but this one seems to
have an interior that’s still at least partly liquid.”

“Why is that a problem?”

“Liquid iron on that scale
would generate huge magnetic fields, like nothing we’ve seen in
our own solar system. Magnetic fields that strong would block almost
all of the cosmic radiation.”

“Oh, I see, yes, that is a
problem. How would the life forms get the energy that they need to
live if all the cosmic radiation were blocked by this giant magnetic
field?”

“Precisely.”

“There’s not a single
known example of a silicon based life form drawing energy from a
source other than cosmic rays.”

“And that’s the
difficulty.”

“Yes, I see that it’s a
very taxing problem.”

“I was wondering, though.
Perhaps we’ve been looking at this all the wrong way.”

“What do you mean?”

“We’ve been looking the
whole time for life forms just like ourselves – silicon and
mercury based. We look for planets that are in just the right
position, far enough away from the star to have liquid nitrogen,
mainly gaseous, or at least vapourous in composition, and with access
to plentiful cosmic radiation. A sort of Goldilocks zone, if you
like.”

“Yes, indeed; just the right
conditions for life to form.”

“But could it not be said
that life on this planet evolved with the sort of chemistry that it
did precisely because that suited the conditions in which it first
came into being? There’s no reason in principle that life has
to be based on silicon and mercury, is there? It could be based on
anything that allows for self replication. All that it really needs,
surely, is an environment that is stable enough to allow complex,
self-replicating molecules to exist for long enough to evolve, but
not so stable that they won’t be created in the first place?
The heat of the star could provide the energy if all the cosmic rays
were blocked.”

“Those are very grand ideas,
but what other form of chemistry could support self-replication? I
know that some experiments recently have suggested that possibly
arsenic could replace mercury in certain conditions, but even those
organisms couldn’t survive the sort of temperatures you’re
talking about on that planet. So far as we know, no living organism
could withstand heat anywhere near enough to satisfy its energy
requirements. That’s the beauty of ionising radiation.”

“I suppose that you must be
right. It was a far-fetched idea. But what of these low-energy
radiation signals?”

“That is the conundrum. But,
wait; didn’t you say that the planet had a liquid iron core?”

“Yes.”

“Could that possibly account
for these signals? We haven’t seen any iron planets in our
solar system; for all we know, all that iron sloshing about could
generate all kinds of interference patterns.”

“Yes – or more likely,
perhaps, the magnetic field is somehow filtering and distorting the
star’s radiation, although I’m not quite sure how that’d
work. Nobody’s done any modelling on that. But that does sound
more plausible than complex life forms on a hot, rocky planet, you’re
right. It’s a pity, though. I did wonder whether this might
have been it.”

“The more that I work on this
project, the more that it seems that we really are alone in the
universe after all.”